This invention relates to an aluminum nitride sintered body, and particularly to a manufacturing method for an aluminum nitride sintered body which has good thermal conductivity.
In recent years, as electronic devices have undergone enormous increases in speed and performance along with decreases in size and weight, the dissipation of the heat generated by semiconductor elements in these devices has become a major problem. In particular, in high-density packaged IC's, LSI's, microwave transistors for microwave and optical communication, laser diodes, and the like, there is a great demand for a base material which has high thermal conductivity.
In the past, alumina sintered bodies have been widely used as electrically-insulating base materials, but their ability to dissipate heat is inadequate for recent electronic devices, and therefore an electrically-insulating base material having improved thermal conductivity is needed.
One material which has been viewed with much interest as a base material having high thermal conductivity is aluminum nitride. Its electrical resistance, dielectric strength, dielectric constant, bending strength, coefficient of thermal expansion, and other properties which are important for an electrically-insulating base material are comparable or superior to those of alumina sintered bodies, and accordingly it has been the subject of extensive research.
However, aluminum nitride is difficult to sinter, particularly alone at normal pressures. For this reason, manufacturing methods for sintered bodies using hot pressing and manufacturing methods for sintered bodies which are performed at normal pressures by the addition of various oxides as auxiliaries are being studied. Among these methods, sintering methods performed at normal pressures are preferable since they are better suited to large-scale production. One such sintering method is that disclosed in Japanese Patent Laid-Open No. 54-100410, which is a sintering method for aluminum nitride in which a sintering auxiliary such as calcium oxide (CaO), barium oxide (BaO), or strontium oxide (SrO) is added. However, the thermal conductivity of an aluminum nitride sintered body obtained by that method is only 50-60 W/mK, and therefore a manufacturing method for an aluminum nitride sintered body having a higher thermal conductivity has been searched for.
Japanese Patent Laid-Open No. 60-151280 discloses a manufacturing method for sintered aluminum nitride in which an acetylide of calcium, magnesium, barium, strontium, or the like is used as an auxiliary, and Japanese Patent Laid-Open No. 60-186478 discloses a sintering method in which a nitride of calcium, magnesium, barium, strontium, or the like is added. However, the auxiliaries which are used in those two methods are extremely unstable in air. For example, calcium acetylide, which is used in No. 60-151280, reacts violently with water. If calcium acetylide having a grain size of finer than 150 mesh is left in air for one hour, all of it will break down to form Ca(OH).sub.2. Furthermore, if calcium nitride, which is used in No. 60-186478, having an average particle diameter of 3 microns is exposed to air, it will immediately break down into Ca(OH).sub.2.
It is conceivable to prevent this breakdown by handling the auxiliaries so that they will not be exposed to water or air, but in actual practice, it is extremely difficult and expensive to prevent breakdown during the various steps (grinding, mixing, forming, dewaxing, and sintering) in the manufacture of a base material.